Pretreatment of metal surfaces with a calcium-containing aqueous agent

ABSTRACT

Described herein is a method for treating a metal surface, such as an aluminum alloy surface, which involves contacting the surface coated with a pretreatment coating comprising fluoride ions with an aqueous agent comprising at least 7 ppm calcium ions. The method reduces fluoride ion content in the pretreatment coating, increases calcium ion content in the pretreatment coating, improves corrosion resistance, such as filiform corrosion resistance, of the metal surface, and/or improves adhesion between the surface and a surface coating, such as a paint, lacquer, adhesive or a bonding agent. The aqueous agent can be a calcium-containing rinse, for example, a solution of a calcium salt. Articles of manufacture comprising metal surfaces treated by the above methods as well as the related manufacturing processes are also described.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.62/089,036, filed Dec. 8, 2014, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates to the fields of material science,material chemistry, surface chemistry, metal manufacturing, aluminumalloys, aluminum manufacturing and related fields. The present inventionprovides novel compositions and processes for surface pretreatment ofmetals, for example, aluminum alloys, in order to improve theircorrosion resistance. The compositions, processes and uses describedherein can be employed in various industries to produce articles ormaterials comprising metal surfaces, such as aluminum alloy surfaces,including, but not limited to, motor vehicle parts or panels,construction or architectural parts or panels, electronic housings,composite and bonded materials and articles, and other products andparts comprising metal surfaces.

BACKGROUND

Articles manufactured from or including metals, such as aluminum alloys,often contain surfaces covered with various types of films or coatings,for example, paints, lacquers or bonding compounds, such as resins,glues or other types of adhesives. One problem associated with the metalsurfaces, such as aluminum alloy surfaces, covered with films orcoatings is filiform corrosion. The term “filiform corrosion” and otherrelated terms typically refer to a type of corrosion occurring at theinterface between metal surfaces and thin films or coatings, includingorganic and inorganic films and coatings. Filiform corrosion has anappearance of randomly or semi-randomly distributed filaments emanatingfrom one or more sources (“heads”) under bulging and/or crackingcoating. These filaments are channels or crevices comprised of corrosionproducts, such as metal salts. Filiform corrosion is initiated byatmospheric water and oxygen supplied to the initial site (which forms a“head”) by osmosis and propagates under the film forming the filaments,which can be referred to as “tails.” Although the damage to a metalsurface caused by filiform corrosion may not be extensive, itdetrimentally affects the coating, including its appearance, functionalproperties and bond with the surface. For example, filiform corrosion ofa painted or aluminum alloy surface may lead to a surface riddled withchannels filled with white aluminum hydroxide precipitate. In anotherexample, filiform corrosion may lead to interfacial failure of ametal/adhesive or metal/bonding compound interface, which, in turn, maylead to a structural failure of an article containing such an interface.Filiform corrosion is associated with exposure to high humidity and alsowith the occurrence of various ions on the metal surface. A number ofapproaches have been employed to reduce filiform corrosion at a metalsurface under a film or coating. One of these approaches is the use ofthe so-called pretreatment coatings or primers. Pretreatment coatingsprovide a stable metal oxide surface that resists filiform corrosion andpromotes adhesion of the film or coating to the aluminum alloy surface.One class of pretreatment coatings are pretreatment coatings containingcombinations of metal ions, such as Ti/Zr pretreatment coatings, whichtie up oxygen at the metal surface in stable oxides that function as anoxygen diffusion barrier.

The formation of Ti/Zr pretreatment involves the hydrolysis ofhexafluorotitanate and hexafluorozirconate to form Ti/Zr oxides, whichproduces free fluoride ions as a byproduct. Although the oxide layerprovides a degree of protection from filiform corrosion and improves thebonding between the aluminum alloy surface and the coating, it isbelieved that the byproduct-free (non-complexed with Ti, Zr or othermetal) fluoride ions lead to filiform corrosion propagation. Thefluoride ions can easily incorporate into the Al oxide layers betweenthe pretreatment coating and the alloy substrate and replace the oxygenin the Al oxide matrix, which eventually causes the dissolution of Aland leads to the corrosion of the alloy surface.

In an attempt to reduce free fluoride ion content, the pretreatmentcoating is typically rinsed after application with deionized water. Thismethod requires large amounts of deionized water to lower fluoride ionlevels. Production of the deionized water and treatment of the spentrinse solution to remove dissolved compounds prior to discharge both addto the costs of the above process and may create significant amounts ofhazardous waste. More generally, improved bonding between aluminum alloysurfaces and various coatings would be beneficial for various industriesand fields. Accordingly, improved processes and compositions forpretreatment of aluminum alloy surfaces are desired.

SUMMARY

The terms “invention,” “the invention,” “this invention” and “thepresent invention,” as used herein, are intended to refer broadly to allof the subject matter of this patent application and the claims below.Statements containing these terms should be understood not to limit thesubject matter described herein or to limit the meaning or scope of thepatent claims below. Covered embodiments of the invention are defined bythe claims, not this summary. This summary is a high-level overview ofvarious aspects of the invention and introduces some of the conceptsthat are further described in the Detailed Description section below.This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification, any or all drawings and each claim.

The present invention provides solutions to problems associated withfiliform corrosion of metal surfaces, such as aluminum alloy surfaces,surfaces covered with organic or inorganic films or coatings, and, moregenerally, with the adhesion of coatings or films (for example, paint oradhesive adhesion). The present invention may be used to improve theadhesion between metal surfaces, such as aluminum alloy surfaces, andthe films or coatings. It may also be used to improve adhesion betweenmetal surfaces and other metal or non-metal surfaces bonded or gluedtogether with bonding compounds or adhesives. The present inventionaddresses these problems by providing anti-corrosion pretreatment on ametal surface, such as an aluminum alloy surface, in which apretreatment coating containing metal and fluoride ions, such as a Ti/Zrpretreatment coating, after its application to the metal surface, suchas the aluminum alloy surface, is contacted with an aqueous agentcontaining calcium ions. The presence of free fluoride ions causes thecorrosion of the metal surface which eventually leads to coatingsdetachment or bonding failure. Calcium ions in the aqueous agent formionic bonds with free fluoride ions in the pretreatment coating. It isunderstood that, as a result of the ionic attraction, fluoride ionsleach out of the pretreatment coating, which simplifies their removalfrom the pretreatment coating, for example, by rinsing the pretreatedsurface. Furthermore, it is also understood that calcium ions from thecalcium-containing aqueous agent migrate into the Ti/Zr coating layer,and ionic bonds are formed between calcium and fluoride ions remainingin the coating layer. Thus formed CaF₂ is insoluble, which is a reasoncalcium ions can be employed to stabilize the free fluoride ions. Thisphenomenon sequesters fluoride ions in insoluble complexes, thuslowering their availability for filiform corrosion propagation. Thesephenomena, which are described according to current understanding andare not intended to limit the present invention, as well as otherphenomena, some of which are discussed further herein, reduce thepropensity of the aluminum alloy surface for filiform corrosion andimprove the bonding between the surface and the coatings or films.Although differences may exist in the adhesion of surface coatings tometal surfaces, such as cosmetic paints, and adhesion of compounds usefor structural bonding (for example, adhesives), the present inventionmay be used to improve adhesion of both surface coatings and adhesion ofbonding compounds.

The improved processes described herein can possess various advantages.For example, they can be less costly than conventional pretreatments,use less water, and produce less hazardous waste than the conventionalpretreatments, such as those employing deionized water rinses. Someembodiments of the present invention are processes for anti-corrosionpretreatment of aluminum alloys that utilize calcium-containing aqueousagents. Compositions of matter related to calcium-containing aqueousagents as well as uses of a calcium-containing aqueous agent in theprocess of anticorrosion pretreatment are also included within theembodiments of the present invention. Some other embodiments of thepresent invention are processes of producing or manufacturing articlesthat comprise coated aluminum alloy surfaces treated by the improvedsurface pretreatment. The present invention also encompasses articlesmanufactured according to the above processes, including materialscontaining aluminum alloy surfaces. Some exemplary embodiments of thepresent invention are summarized below.

One exemplary embodiment of the present invention is a method fortreating a metal surface coated with a pretreatment coating comprisingfluoride ions. The method includes a step of contacting the metalsurface one or more times with an aqueous agent comprising at least 7ppm calcium ions. Another exemplary embodiment of the present inventionis a method for pretreatment of a metal surface, which includes thesteps of: coating the metal surface with a pretreatment coating; and,contacting the metal surface coated with the pretreatment coating withan aqueous agent comprising at least 7 ppm calcium ions. One moreexemplary embodiment of the present invention is a method of improvingcorrosion resistance of a metal surface, which includes the steps ofcoating the metal surface with a pretreatment coating and contacting themetal surface coated with the pretreatment coating with an aqueous agentcomprising at least 7 ppm calcium ions. In the embodiments of thepresent invention, the metal surface can be an aluminum alloy surface,for example, a surface of a 2xxx, 3xxx, 5xxx, 6xxx or 7xxx aluminumalloy. In the embodiments of the present invention, the pretreatmentcoating can be a Ti/Zr or Zr/Cr coating. For example, the pretreatmentcoating can be hexafluorotitanate, hexafluorozirconate or chromiumsulfate coating. According to the embodiments of the present invention,the aqueous agent can be a solution of a calcium salt, for example, acalcium carbonate, a calcium phosphate, a calcium nitrate or a calciumsulfate. The aqueous agent can contain calcium (Ca²⁺) ions in an amountof at least about 7 ppm (about 7 ppm or above), for example, at leastabout 7.5 ppm, at least about 8.0 ppm, at least about 8.5 ppm, at leastabout 9 ppm, or at least about 9.5 ppm. In some embodiments, the aqueousagent can contain calcium ions in an amount of from about 7.5 ppm toabout 500 ppm, (e.g., from about 8 ppm to about 450 ppm, from about 8.5ppm to about 400 ppm, from about 9.0 ppm to about 350 ppm, from about9.5 ppm to about 300 ppm, from about 10 ppm to about 250 ppm, from about20 ppm to about 200 ppm, from about 50 ppm to about 100 ppm, or fromabout 10 ppm to about 50 ppm). In some embodiments, the aqueous agentcan contain calcium ions in a range of from about 7.5-9.8 ppm. In someembodiments, the aqueous agent can contain calcium ions at about 7.5ppm. In some other embodiments, the aqueous agent can contain calciumions at saturation. In some exemplary embodiments, the aqueous agent isa saturated solution of calcium carbonate.

The step of contacting the metal surface with the aqueous agent in theprocesses according to the embodiments of the present invention caninclude one or more of immersing the metal surface in the agent, rinsingthe metal surface with the agent, rolling the agent onto the metalsurface, or spraying the metal surface with the agent. After the step ofcontacting the metal surface with the aqueous agent according to theembodiments of the present invention, the fluoride ion content can bereduced in the pretreatment coating, and/or calcium ion content can beincreased in the pretreatment coating. In some embodiments, the metalsurface is rinsed with the aqueous agent in the contacting step, and theweight of the pretreatment coating after the contacting step is greaterin comparison to a metal surface coated with the pretreatment coatingrinsed with deionized water. The embodiments of the present inventioncan include, after the contacting step, a step of applying to the metalsurface one or more of a paint, a lacquer, an adhesive, a glue or abonding compound.

The embodiments of the present invention include articles of manufacturecomprising a metal surface treated by the methods according to theembodiments of the present invention. Some examples of such articles ofmanufacture are an aluminum alloy sheet, a motor vehicle panel, anautomotive panel, an electronics panel, an architectural panel or amaterial comprising an aluminum alloy surface. Processes ofmanufacturing the articles of manufacture which include the methodsaccording to the embodiments of the present invention are alsoencompassed by the embodiments of the present invention. Otherembodiments, objects and advantages of the present invention will beapparent from the following detailed description of embodiments of theinvention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A shows a line plot illustrating depth profiling x-rayphotoelectron spectroscopy (XPS) data for Ti after rinsing pretreatedaluminum alloy samples with deionized water, tap water and calciumcarbonate solution.

FIG. 1B shows a line plot illustrating depth profiling x-rayphotoelectron spectroscopy (XPS) data for Zr after rinsing pretreatedaluminum alloy samples with deionized water, tap water and calciumcarbonate solution.

FIG. 2A shows a line plot illustrating depth profiling XPS data for Siafter rinsing pretreated aluminum alloy samples with deionized water,tap water and calcium carbonate solution.

FIG. 2B shows a line plot illustrating depth profiling XPS data for Oafter rinsing pretreated aluminum alloy samples with deionized water,tap water and calcium carbonate solution.

FIG. 3A shows a line plot illustrating depth profiling XPS data for Caafter rinsing pretreated aluminum alloy samples with deionized water,tap water and calcium carbonate solution.

FIG. 3B shows a line plot illustrating depth profiling XPS data for Fafter rinsing pretreated aluminum alloy samples with deionized water,tap water and calcium carbonate solution.

DETAILED DESCRIPTION

Described herein are pretreatment compositions and improved methods ofpretreating aluminum alloy surfaces, which also can be applied to thepretreatment of other metal surfaces. The improved pretreatment lowersthe concentration of free fluoride ions at the surface of a metal, suchas an aluminum alloy surface, coated with the pretreatment coating, aswell as in the pretreatment coating. By reducing the content of freefluoride ions, the improved pretreatment reduces and/or inhibitspropagation of filiform corrosion on a metal surface. By reducing thefiliform corrosion, the improved anticorrosion pretreatment generallyimproves the bond between a film or coating (for example, paint oradhesive) and the metal surface. In some exemplary embodiments, theimproved anticorrosion pretreatment leads to improved bond durabilitywhen adhesive compounds are used to bond metal surfaces with other metalor non-metal surfaces. In some other exemplary embodiments, the improvedanticorrosion pretreatment leads to more durable and stable bondsbetween a metal surface and a coating applied on the metal surface, suchas a coating or paint. The embodiments of the present invention includemethods for treating metal surfaces, such as aluminum alloy surfaces.The methods are performed with the goal of inhibiting corrosion, such asfiliform corrosion, of the metal surfaces, such as aluminum alloysurfaces, covered with an organic or inorganic coating or film,including protective and/or decorative coatings, such as lacquers orpaints, adhesive or bonding compounds, such as glues or resins, or othertypes of films, coatings or compounds. The methods of the presentinvention can therefore be referred to as anticorrosion pretreatment ormethods to improve corrosion resistance or other related terms.

The methods according to some embodiments of the present invention canalso be described as surface pretreatment methods, methods of treatingaluminum alloy surfaces, methods of treating metal surfaces or otherrelated terms. The methods of the invention comprise one or more stepsof contacting a metal surface, such as an aluminum alloy surface, whichhas been treated by a pretreatment agent comprising metal ions andfluoride ions, such as Zr, Ti, Cr, Ce, or V-based agents, with anaqueous agent comprising calcium ions (Ca²⁺). The aqueous agent used inthe methods of the present invention may contain at least 7 ppm Ca²⁺ions in an aqueous solution, and can be referred to as acalcium-containing agent. As discussed above, the exposure of thepretreatment coating layer to the calcium-containing agent leads toformation of ionic bonds between calcium ions originating in thecalcium-containing agent and free fluoride ions (F) found in thepretreatment coating layer. Due to the ionic attraction to calcium ions,fluoride ions leach out to the surface of the pretreatment coating,while calcium ions from the agent migrate into the pretreatment coatinglayer, sequestering fluoride ions remaining in the layer in ioniccomplexes, such as CaF₂ complexes, which are poorly soluble. The amountof free fluoride ions found in the pretreatment coating layer is therebyreduced, which alleviates filiform corrosion propagation under the filmcoating applied onto the metal surface. Additional phenomena may beinvolved, which also inhibit filiform corrosion. For example, thepresence of calcium ions at the metal surface may increase the pH at thesurface. Higher pH, particularly in the alkaline range, inhibitspropagation of filiform corrosion.

The phenomenon of filiform corrosion described above is intended to aidin the description and the understanding of the embodiments of thepresent invention. While the pretreatment processes according theembodiments of the present invention may alleviate filiform corrosion,the advantages of using the methods of the present invention are notlimited to reducing, inhibiting, or alleviating filiform corrosion orits propagation. Based on the experimental data, a contact with acalcium-containing agent may increase the weight of the pretreatmentcoat on a metal surface, improving bond durability with the finalcoating. More generally, the pretreatment processes according to theembodiments of the present invention improve durability of the coatingsapplied onto metal surfaces and/or improve durability between thecoating and the metal surface. The pretreatment processes according tothe embodiments of the present invention also improve the stability ofthe interface between a metal surface and an organic or inorganic filmor coating applied onto it and/or improve the bond between metalsurfaces and other metal or non-metal components bonded to such surfaceswith bonding compounds or adhesives, which leads to reduced failure ofthe above interfaces. Furthermore, the pretreatment processes accordingto the embodiments of the present invention improve adhesion between afilm or coating and a metal surface, and reduce the possibility ofadhesion failure between metal surfaces and other metal or non-metalcomponents bonded to them with bonding or adhesive compounds metal ornon-metal surfaces.

The metal surfaces suitable for pretreatment according to theembodiments of the present invention include surfaces of various alloyedand non-alloyed metals, for example, iron, magnesium, zinc, copper,brass and aluminum and their alloys. The aluminum alloy surfacessuitable for pretreatment according to the embodiments of the presentinvention include surfaces comprised of aluminum alloyed with variouselements, such as Fe, Mn, Si, Mg, Cu, etc. as well as surfaces comprisedof substantially pure aluminum. In other words, the term “aluminum alloysurface” is not intended to be limited by the type of an aluminum,alloyed or unalloyed. Some examples of aluminum alloys suitable for thepretreatment according to the embodiments of the present invention are2xxx, 3xxx, 5xxx, 6xxx or 7xxx aluminum alloys (according to AluminumAssociation (AA) Designation). The term “surface” as used hereingenerally means an outer part of a quantity of a metal, such as analuminum alloy. In some cases, a surface may be an outer part whensubjected to the pretreatment, but later may be on the inside of anobject or a material. For example, a multilayer composite comprising oneor more metal layers may contain, on the inside, surfaces treatedaccording to the processes of the present invention and subsequentlybonded with other metal or non-metal surfaces.

As discussed above, the methods according to some embodiments of thepresent invention involve a metal surface, such as an aluminum alloysurface, that has been subjected to pretreatment coating (“pretreated”)with a pretreatment coating or agent comprising metal ions and fluorideions. The description of pretreatment coatings provided above isintended to aid in the understanding of the present invention. Examplesof pretreatment coatings comprising metal ions and fluoride ions includeTi/Zr and Zr/Cr coatings. Some other non-limiting examples of thepretreatment coatings are hexafluorotitanate, hexafluorozirconate andchromium sulfate coatings, conversion coatings based on chromium(chromium sulfate or chromate—Cr(VI)—e.g., K₂CrO₄), cerium (ceriumchloride/hydroxide, cerium nitrate) coatings, vanadate (vanadatesulfate) coatings, or manganese (for example, manganese phosphate)coatings.

Pretreatment coatings are applied to aluminum alloy surfaces usingappropriate processes, such as etching, pretreating, rinsing, andcuring. A pretreatment coatings may be characterized by the content ofconstituent elements, such as Ti, Zr, etc. Pretreatment coating forms apretreatment film upon application, but the terms “coating” and “film”can be used interchangeably in this context. A pretreatment coating canbe characterized by a thickness of the film formed by the pretreatmentcoating, for example, it can be about 20 nm to about 10 μm thick (e.g.,about 25 nm to about 8 μm, about 50 nm to about 6 μm, about 75 nm toabout 4 μm, about 100 nm to about 2 μm, about 125 nm to about 1 μm,about 150 nm to about 800 nm, about 175 nm to about 600 nm, about 200 nmto about 575 nm, about 225 to about 550 nm, about 250 nm to about 500nm, about 275 nm to about 475 nm, about 300 nm to about 450 nm, about325 nm to about 425 nm, or about 350 nm to about 400 nm). For example,the film formed by the pretreatment coating can be about 20 nm, about 30nm, about 40 nm, about 50 nm, about 60 nm, about 70 nm, about 80 nm,about 90 nm, about 100 nm, about 200 nm, about 300 nm, about 400 nm,about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm,about 1 μm, about 2 μm, about 3 μm, about 4 μm, about 5 μm, about 6 μm,about 7 μm, about 8 μm, about 9 μm, or about 10 μm. The processes of thepresent invention may improve the performance of the pretreatmentcoating, for example, by (1) reducing free fluoride ion content in thefilm (2) stabilizing the free fluoride ions remaining in the coating and(3) increasing the coat weight constituent elements in the film, forexample, Ti and Zr. When subjected to the processes according to theembodiments of the present invention, the pretreatment coating on analuminum alloy surface may contain detectable levels of calcium, forexample 7-500 ppm or 10-50 ppm. It is to be understood that one or moresteps (e.g., two or more steps, three or more steps, four or more steps,etc.) of applying a pretreatment coating may be included in theprocesses of the present invention, and that one or more types ofpretreatment coating (e.g., two or more types of pretreatment coating,three or more types of pretreatment coating, four or more types ofpretreatment coating, etc.) may be employed.

As discussed above, the processes according to the embodiments of thepresent invention involve one or more steps of contacting the aluminumalloy surface coated with a pretreatment coating with an aqueouscalcium-containing agent. An aqueous calcium-containing agent containscalcium (Ca²⁺) ions in an amount of at least about 7 ppm (7 ppm orabove, which can also be expressed as >7 ppm), for example, at leastabout 7.5 ppm, at least about 8.0 ppm, at least about 8.5 ppm, at leastabout 9 ppm, or at least about 9.5 ppm. In some embodiments, the aqueousagent can contain calcium ions in an amount of from about 7.5 ppm toabout 500 ppm, from example, from about 8 ppm to about 450 ppm, fromabout 8.5 ppm to about 400 ppm, from about 9.0 ppm to about 350 ppm,from about 9.5 ppm to about 300 ppm, from about 10 ppm to about 250 ppm,from about 20 ppm to about 200 ppm, from about 50 ppm to about 100 ppm,or from about 10 ppm to about 50 ppm. In some embodiments, the aqueousagent can contain calcium ions in a range of from about 7.5-9.8 ppm. Insome embodiments, the aqueous calcium-containing agent can containcalcium ions at about 7.5 ppm. In some embodiments, an aqueouscalcium-containing agent contains calcium ions at saturation.

Examples of aqueous agents include an aqueous solution, a sol, or a gel.An aqueous agent used in the pretreatment methods of the presentinvention may contain calcium salts, such as calcium carbonate, calciumnitrate, calcium sulfate, calcium phosphate, etc. In addition to calciumions and/or salts, an aqueous agent may contain other metal ions orsalts, as well as other components. One example of an aqueous agent is asaturated solution of a calcium salt, such as CaCO₃. Another example isan aqueous solution containing calcium ions and detectable levels of oneor more of Al, Mg, Si, and Mn. Embodiments of the present inventionencompass aqueous agents described herein as well as their uses in theprocesses of the present invention.

Various suitable methods may be employed in the processes of the presentinvention for contacting a calcium-containing aqueous agent with apretreated metal surface, such as an aluminum alloy surface. Bringingthe metal surface, such as the aluminum alloy surface, and thecalcium-containing aqueous agent into contact may also be described asexposing the surface to the aqueous agent, or applying the aqueousagent. Examples of methods that may be used to bring the metal surface,such as the aluminum alloy surface, and the calcium-containing agentinto contact include, but are not limited to, immersing (for example, byimmersion of the surface into a bath or other type of vessel containingthe calcium-containing agent), rinsing or spraying, or rolling the agentonto the surface. Suitable methods and conditions are selected andoptimized based on various considerations, such as the desired extent ofcalcium penetration into the pretreatment coating, the extent offluoride ion reduction in the pretreatment coating, the type of theagent used and/or the type of the surface being treated. The ease ofintegrating the pretreatment processes of the present invention into themanufacturing processes and lines is also taken into account. One ormore contacting steps may be employed. For example, one, two, three,four, five or more steps are possible. In some embodiments of theprocesses according to the present invention, more than one step ofapplying a pretreatment coating may be included, in which case, acalcium-containing agent may be applied one or more times after eachstep of the pretreatment coating or after some (one or more) of thesteps. Contact of the pretreated aluminum alloy surface with thecalcium-containing agent may be conducted at various temperatures, forexample at a temperature from approximately 15° C. to 85° C. Theduration of the contact of the pretreated metal surface, such as thepretreated aluminum alloy surface, with the calcium-containing agent mayalso vary. In some embodiments, the contact duration can range fromseveral seconds (e.g., two or more seconds, three or more seconds, fouror more seconds, five or more seconds, six or more seconds, seven ormore seconds, eight or more seconds, nine or more seconds, 10 or moreseconds, 15 or more seconds, 20 or more seconds, 25 or more seconds, or30 or more seconds) to one or more minutes (e.g., two or more minutes,three or more minutes, four or more minutes, five or more minutes, sixor more minutes, seven or more minutes, eight or more minutes, nine ormore minutes, 10 or more minutes, 11 or more minutes, 12 or moreminutes, 13 or more minutes, 14 or more minutes, 15 or more minutes, 16or more minutes, 17 or more minutes, 18 or more minutes, 19 or moreminutes, or 20 or more minutes). For example, the duration of thecontact of the pretreated metal surface with the calcium-containingagent can range from about 2 seconds to 20 minutes, from about 10seconds to about 15 minutes, from about 30 seconds to about 10 minutes,or from about 1 minute to 5 minutes. The selected duration, which mayalso be referred to as “dwell time,” may depend on various factors, suchas the type of the pretreatment coating, concentration of thepretreatment agent or the method of application.

After the step of contacting the pretreated metal article, such as analuminum alloy article, with the calcium-containing aqueous agent, theprocesses of the present invention may further contain one or more steps(two or more, three or more, four or more, etc.) of applying one or morefilms or coatings. The embodiments of the present invention areapplicable to either organic and inorganic films or coatings. Somenon-limiting examples of inorganic coatings are zinc phosphate,zirconium oxide, and E-coat. Some non-limiting examples of organiccoatings are films (such as protective or decorative films), paints,lacquers, adhesives, bonding compounds, glues and resins, or primers. Itis to be understood that more than one type of coating (e.g., one ormore, two or more, three or more, etc.) may be employed.

Embodiments of the present invention include processes of producing ormanufacturing articles that comprise coated metal surface(s), such asaluminum alloy surface(s), treated by the surface pretreatment processesdiscussed above. The processes may be employed in various industries,including motor vehicle, aircraft or electronics manufacturing,automotive industry, transportation industry, or more generally, in anyindustry where adhesive bonds of metal parts, such as aluminum alloyparts, are used.

The present invention also encompasses articles and materialsmanufactured by the above processes described herein. Examples of thearticles include motor vehicle parts or panels, ship or aircraft partsor panels, construction or architectural parts or panels and electronichousing parts. Other examples of materials include composite and bondedmaterials, including metals, such as aluminum alloys, layered compositesor laminates including aluminum layers adhered or bonded to aluminum orother types of layers, and clad or monolithic aluminum alloy sheets,such as those containing, for example, 2xxx, 3xxx, 5xxx, 6xxx and 7xxxaluminum alloys. More generally, the present invention encompassesarticles and materials that are manufactured by the processes describedherein and include coated or bonded metal surfaces, such as aluminumalloy surfaces, or articles and other products or parts comprisingcoated or bonded metal surfaces, such as aluminum alloy surfaces.

Advantages afforded by the embodiments of the present invention includethose discussed above. Further advantages of the embodiments of thepresent invention include improved methods producing a coated metalarticle, such as an aluminum article, with at least the same durabilityand corrosion resistance as the conventional processes, while reducingthe costs and the hazardous waste. In one example, when rinsing apretreated aluminum surface with a calcium-containing solution insteadof rinsing with deionized water, a significant reduction of water usagemay be achieved, because less rinsing agent is required to achieve atleast a comparable reduction in fluoride levels. In another example, tapwater may be employed as a calcium-containing rinse agent.

The following examples will serve to further illustrate the presentinvention without, at the same time, however, constituting anylimitation thereof. On the contrary, it is to be clearly understood thatresort may be had to various embodiments, modifications and equivalentsthereof which, after reading the description herein, may suggestthemselves to those skilled in the art without departing from the spiritof the invention.

EXAMPLES Example 1 Aluminum Alloys Pretreated with Ti/Zr-BasedPretreatment Film

An experimental study was conducted to test a hypothesis that Ca²⁺ ionsin rinsing tap water form ionic bonds with the excessive F ions presentin a Ti/Zr-based pretreatment film. If this phenomenon takes place, itmay stabilize F ions and reduce the possibility of corrosion andadhesion failure of the pretreatment film. The study was conducted usingsamples of AA5754 and AA6111 aluminum alloys. Three types of rinses weretested, including deionized (DI) water, tap water, and an artificiallyprepared calcium-containing rinse (“calcium rinse”). The calcium rinsewas a saturated solution of CaCO₃ in deionized water at 65° C. The CaCO₃rinse was prepared by adding CaCO₃ to DI water to a saturation level andthen purging the resulting solution with CO₂. The results of inductivelycoupled plasma (ICP) analysis of different rinses are shown in Table 1.In particular, the concentration of calcium CaCO₃ rinse was determinedto be about 15 ppm. The concentration of calcium in tap water wasdetermined to be about 7.5-9.8 ppm (see Table 1).

TABLE 1 ICP of calcium-containing rinses ICP results in ppm Final rinseCa Mg Na Si S Fe DI <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Tap 7.5-9.8 1.9 7.13.0 5.4 <0.1 Ca Saturated <0.1 <0.1 <0.1 <0.1 <0.1

The aluminum alloy samples were prepared as follows. Mill-finishedAA5754 and AA6111 samples were subjected to the following sequentialsteps: (1) acidic etching in a solution of ferric sulfate and sulfuricacid, (7%) at 40-80° C. for 5-30 seconds; (2) rinsing in DI water at 65°C. for 8 seconds; (3) pretreatment in the pretreatment solution at40-80° C. for 4-30 seconds; (4) air drying for 5-30 seconds at roomtemperature; (5) final rinsing by immersing each sample in one of thethree different rinses at 40-80° C. for 4-30 seconds; and (6) air dryingwith clean compressed air. The titanium coat weight for each sample wasdetermined by X-ray fluorescence (XRF). A description of XRF analysisprotocol is provided, for example, in “S2 Ranger. SpectrometrySolutions.” published in 2013 by Bruker AXS (Germany). The results ofthe XRF analysis are summarized in Table 2.

TABLE 2 Ti coat weight determination Final Ti coat weight (mg/m²) rinseAA5754 AA6111 DI 9.5 11.5 Tap 9.1 9.4 Ca 11.0 13.4

It was determined that the relative Ti coat weight was greater forAA6111 samples than for AA5754 samples. For both alloys, the relative Ticoat weights increased in the following sequence of rinses: tap waterrinse<DI water rinse<calcium-containing rinse.

Elemental depth profiling of AA6111 alloy samples was performed usingx-ray photoelectron spectrometry (XPS). A description of XPS protocolsis provided, for example, in “Axis Ultra. Operators Manual” published in1998 by Kratos Analytical (UK). The results are illustrated in FIGS. 1A,1B, 2A, 2B, 3A, and 3B. As illustrated in FIGS. 1A and 1B, the greatestsignal for Ti and Zr at the Ti/Zr-pretreated sample surface wasregistered after the calcium rinse, which is consistent with greatercoat weight registered with the XRF determination. As illustrated inFIGS. 2A and 2B, the samples rinsed with the calcium rinse also showedstronger signals of both Si and O, in comparison with DI-rinsed samples,which indicates that a greater pretreatment coat weight was present onthe samples rinsed with the calcium rinse. As shown in FIGS. 3A and 3B,a much stronger signal of calcium was detected on the Ti/Zr-pretreatedAA6111 after the calcium rinse than on the other two samples. No calciumwas detected on the DI water-rinsed sample. As also illustrated by FIGS.3A and 3B, for the DI water-rinsed sample, fluoride tended to be rinsedout of the coating and then enriched at the Ti/Zr surface; in contrast,fluoride in the sample rinsed with the calcium rinse was stable anddistributed through the coating. The above results indicate that freefluoride in the Ti/Zr coating leached out from Ti/Zr coating into thecalcium rinses, and that free F in the coating was sequestered in thefilm by calcium that migrated into the film from the rinse. The aboveresults also indicate that a greater weight of the pretreatment coatingwas achieved by using calcium-containing rinses, signaling improvedbonding between the pretreatment coating and the aluminum alloy surface.

The above results indicate that a calcium-containing rinse reduced freefluoride ion content in the pretreatment coating from approximately 7%(atomic concentration) to 5%, as illustrated by FIG. 3B, and increasedthe coat weight of Ti (from an atomic concentration of 3% to 5%) and Zr(from an atomic concentration of 1% to 1.4%), as illustrated by FIG. 1Aand FIG. 1B.

Example 2 Effect of Various Rinses on a Ti/Zr-Based Pretreatment Film

An experimental study of the effects of various rinses on a Ti/Zr-basedpretreatment film was conducted. The study was conducted using samplesof AA5754 and AA6111 aluminum alloys. Three types of rinses were tested,including deionized (DI) water, Georgia tap water, and artificiallyprepared calcium-containing rinses, which were prepared as solutions ofCa(HCO₃)₂, Ca(H₂PO₄)₂, CaSO₄, Ca(NO₂)₂ and Ca(NO₃)₂ in deionized waterat 65° C. Each solution had a Ca²⁺ concentration of 200 ppm. Aluminumalloy samples were etched and pretreated as described in Example 1,except for the final rinse step. Different rinses were used on thepretreated samples for the same periods of time. Titanium coat weightfor each sample was determined by X-ray fluorescence (XRF) and thepolymer coat weight was determined by UV-visible spectroscopy (UV/vis).The results of the XRF and UV/vis analysis are summarized in Table 3.For AA6111, the coat weights of both Ti and polymer showed a dependenceon the type of calcium salt used in the rinse. The samples rinsed withCa(HCO₃)₂-based rinse showed the highest Ti coat weight but the lowestpolymer weight, while the samples rinsed with Ca(NO₃)₂-based rinseshowed the lowest Ti weight, but the highest polymer weight.

Stress durability tests were conducted, and the results of these testsare also summarized in Table 3. Briefly, two aluminum alloy laps werebonded using the adhesive to form a joint. Six of these lap joints wereconnected by fasteners in a series and a tensile strength of 2400±25 Nwas applied to the series of joints. The samples were exposed to a humidatmosphere (RH>90%) for 22 hours, immersed in a 5 wt. % solution of NaClfor 1 hour, and air-dried for 1 hour. The above treatment represents onecycle, and bond durability was determined by the number of cycles thesamples pass before they break.

TABLE 3 Experimental results of the testing. Stress testing results forjoints 1-6 Ti coat Polymer coat 1 6 weight weight Final rinse (top) 2 34 5 (bottom) MCTF* (mg/m²) (mg/m²) Ca(CHO₃)₂ 8 8 8 8 8 6 8 21.3 6.2Ca(H₂PO₄)₂ 25 25 25 25 25 25 25 16.2 6.5 CaSO₄ 25 25 25 25 25 25 25 17.67.3 Ca(NO₂)₂ 25 25 25 25 25 25 25 15.2 9.0 Ca(NO₃)₂ 10 10 10 10 5 9 911.3 10.7 Georgia tap water 25 25 25 25 25 25 25 16.3 7.0 DI water 25 2525 25 25 25 25 18.1 6.2*MCTF=mean cycle to failure

Table 3 shows the dependence of the stress durability results for theAA6111 samples on the calcium-containing agents used in the final rinsestep. The joints were in vertical position during the stress durabilitytesting, and numbered 1 through 6, top to bottom. The samples rinsedwith Ca(HCO₃)₂ and Ca(NO₃)₂-based rinses failed after 8-10 cycles, whilethe rest of the samples passed 25 cycles. The stress durability testingshowed that the choice of salt employed in the rinse solution influencesbond durability.

Example 3

A stress durability test was used to assess the effect of thepretreatment and adhesive on bond durability. The study was conductedusing a sample of an AA6111 aluminum alloy including a Ti/Zr-basedpretreatment film. The aluminum alloy samples were etched and pretreatedas described in Example 1. Different rinses were used on the pretreatedsamples for rinse times of 10 seconds. Three types of rinses weretested, including deionized (DI) water, Georgia tap water, andartificially prepared calcium-containing rinses, which were prepared assolutions of Ca(HCO₃)₂, Ca(NO₃)₂, Ca(H₂PO₄)₂, Ca(NO₂)₂, and CaSO₄, indeionized water at 65° C. Each solution had a Ca²⁺ concentration of 200ppm.

In the stress durability test, a set of 6 lap joints/bonds wereconnected in sequence by bolts and positioned vertically in a 100%relative humidity (RH) humidity cabinet. The temperature was maintainedat 50±2° C. A tensile load of 2.4 kN was applied to the bond sequence.The stress durability test is a cyclic exposure test that is conductedfor up to 45 cycles. Each cycle lasts for 24 hours. In each cycle, thebonds are exposed in the humidity cabinet for 22 hours, then immersed in5% NaCl for 15 minutes, and finally air-dried for 105 minutes. Upon thebreaking of three joints, the test is discontinued for the particularset of joints. The completion of 45 cycles indicates that the set ofjoints passed the bond durability test. The test results are shown belowin Table 4. In Table 4, each of the joints are numbered 1 through 6,where joint 1 is the top joint and joint 6 is the bottom joint whenoriented vertically. “Break” in the table indicates that the joint wasbroken during the particular cycle as indicated by the number in thesame cell. “Intact” means that the joint remained intact after thenumber of cycles indicated in the same cell. “Intact*” means that thebonds did not break, but were removed from the test during the cycleindicated by the number in the cell because three other bonds in thesequence had broken.

TABLE 4 Stress durability test Final rinse 1-top 2 3 4 5 6-bot MCTF*Ca(HCO₃)₂  8  8  8  8  8  6 8 Intact* Intact* Break Break Intact* BreakCa(NO₃)₂ 10 10 10 10  5  9 9 Intact* Intact* Intact* Break Break BreakCa(H₂PO₄)₂ 41 41 41 41 25 35 37 Intact* Intact* Intact* Break BreakBreak Ca(NO₂)₂ 45 45 45 45 20 19 37 Intact Intact Intact Intact BreakBreak DI 45 45 45 36 45 25 40 Intact Intact Intact Break Intact BreakCaSO₄ 45 45 45 45 45 24 42 Intact Intact Intact Intact Intact Break Tap45 45 45 45 45 25 42 Intact Intact Intact Intact Intact Break *MCTF =mean cycle to failure

The results above demonstrate that the final rinse can be critical tothe bond durability. Table 4 shows that the final rinse performed withdifferent calcium salts exhibits varying bond durability performance.The bonds rinsed with CaSO₄-enriched water and Georgia tap waterprovided the highest mean cycle to failure and only one broken bond.Ca(NO₂)₂ and DI water each resulted in two broken bonds. Ca(HCO₃)₂,Ca(NO₃)₂, and Ca(H₂PO₄)₂ each resulted in three broken bonds and did notcomplete the nominal requirement of 45 cycles. The results show that tapwater as the final rinse maintains or improves the pretreatmentperformance, as compared to DI water. In addition, the particular anionsof the Ca²⁺ salts affect the bond durability performance.

Table 5 shows the stress durability performance of the pretreated AA6111samples with a rinse using solutions of different Ca²⁺ salts, followedby an optional additional rinse step in DI water for 5 seconds. Each ofthe Ca²⁺ salt solutions had a Ca²⁺ concentration of 200 ppm. The resultsare shown in Table 5. In Table 5, each of the joints are numbered 1through 6, where joint 1 is the top joint and joint 6 is the bottomjoint when oriented vertically. “Break” in the table indicates that thejoint was broken during the particular cycle as indicated by the numberin the same cell. “Intact” means that the joint remained intact afterthe number of cycles indicated in the same cell. “Intact*” means thatthe bonds did not break, but were removed from the test during the cycleindicated by the number in the cell because three other bonds in thesequence had broken.

TABLE 5 Extra Ti weight Stress durability test Final rinse rinse (mg/m²)1-top 2 3 4 5 6-bot MCTF* Ca(HCO₃)₂ n/a 21.3  8  8  8  8  8  6 8 Intact*Intact* Break Break Intact* Break Ca(NO₃)₂ n/a 11.3 10 10 10 10  5  9 9Intact* Intact* Intact* Break Break Break Ca(H₂PO₄)₂ n/a 16.2 41 41 4141 25 35 37 Intact* Intact* Intact* Break Break Break Ca(HCO₃)₂ DI 12.845 40 45 45 35 45 43 Intact Break Intact Intact Break Intact CaSO₄ n/a17.6 45 45 45 45 45 24 42 Intact Intact Intact Intact Intact BreakCa(H₂PO₄)₂ DI 14.9 45 45 45 45 45 30 43 Intact Intact Intact IntactIntact Break Ca(NO₃)₂ DI 15.9 45 45 45 45 34 45 43 Intact Intact IntactIntact Break Intact CaSO₄ DI 15.5 45 45 45 45 45 45 45 Intact IntactIntact Intact Intact Intact *MCTF = mean cycle to failure

As shown in Table 5, the bonds lasted for more cycles and theperformance was significantly improved for the samples rinsed with Ca²⁺solutions and additionally rinsed with DI water. This is attributed tothe existence of pretreatment residues that were not tightly adhered tothe substrate, as shown by the Ti coat weight drop by approximately 2mg/m² after the extra DI water rinse.

All patents, patent applications, publications, and abstracts citedabove are incorporated herein by reference in their entirety. Variousembodiments of the invention have been described in fulfillment of thevarious objectives of the invention. It should be recognized that theseembodiments are merely illustrative of the principles of the presentinvention. Numerous modifications and adaptations thereof will bereadily apparent to those of skill in the art without departing from thespirit and scope of the invention as defined in the following claims.

What is claimed is:
 1. A method for treating a metal surface,comprising: contacting a metal surface one or more times with an aqueousagent comprising at least about 7 ppm calcium ions, wherein the metalsurface is coated with a pretreatment coating comprising fluoride ions.2. A method for pretreating a metal surface, comprising: coating a metalsurface with a pretreatment coating; and contacting the metal surfacecoated with the pretreatment coating with an aqueous agent comprising atleast 7 ppm calcium ions.
 3. A method of improving corrosion resistanceof a metal surface, comprising: coating a metal surface with apretreatment coating; and, contacting the metal surface coated with thepretreatment coating with an aqueous agent comprising at least 7 ppmcalcium ions.
 4. The method of claim 1, wherein the metal surfacecomprises an aluminum alloy surface.
 5. The method of claim 4, whereinthe aluminum alloy surface comprises a surface of a 2xxx, 3xxx, 5xxx,6xxx or 7xxx aluminum alloy.
 6. The method of claim 1, wherein thepretreatment coating comprises a Ti/Zr or Zr/Cr coating.
 7. The methodof claim 1, wherein the pretreatment coating comprises ahexafluorotitanate, hexafluorozirconate or chromium sulfate coating. 8.The method of claim 1, further comprising, after the contacting step,applying to the metal surface one or more of a paint, a lacquer, anadhesive, a glue or a bonding compound.
 9. The method of claim 1,wherein the aqueous agent comprises a solution of a calcium salt. 10.The method of claim 9, wherein the calcium salt comprises a calciumcarbonate, a calcium phosphate, a calcium nitrate or a calcium sulfate.11. The method of claim 1, wherein the aqueous agent comprises asolution of calcium carbonate.
 12. The method of claim 11, wherein theaqueous agent comprises a saturated solution of calcium carbonate. 13.The method of claim 1, wherein the aqueous agent comprises calcium ionsin an amount of at least about 7.5 ppm.
 14. The method of claim 1,wherein the aqueous agent comprises about 7.5 ppm to 9.8 ppm of calciumions.
 15. The method of claim 1, wherein the aqueous agent comprisescalcium ions at saturation.
 16. The method of claim 1, wherein the stepof contacting the metal surface with the aqueous agent comprises one ormore of immersing the metal surface in the agent, rinsing the metalsurface with the agent, rolling the agent onto the metal surface, orspraying the metal surface with the agent.
 17. The method of claim 1,wherein fluoride ion content is reduced in the pretreatment coatingafter the contacting step or wherein the calcium ion content isincreased in the pretreatment coating after the contacting step.
 18. Themethod of claim 1, wherein the metal surface is rinsed with the aqueousagent in the contacting step, and the weight of the pretreatment coatingafter the contacting step is greater in comparison to a metal surfacecoated with the pretreatment coating rinsed with deionized water.
 19. Anarticle of manufacture comprising a metal surface treated by the methodof claim
 1. 20. The article of manufacture of claim 19, wherein thearticle is an aluminum alloy sheet, a motor vehicle panel, an automotivepanel, an electronics panel, an architectural panel or a materialcomprising an aluminum alloy surface.